Brown fat, also called brown adipose tissue, helps maintain your body temperature when you get too cold. It’s the same fat that bears use to stay warm when they hibernate.
Babies are born with a lot of brown fat behind their shoulder blades. Newborns can’t shiver, which is one of the ways the body creates heat. Brown fat acts as a built-in heater. You lose most of it as you get older and form a shiver response to cold temperatures.
Brown Fat vs. White Fat
You have two main types of fat. White fat builds up when you take in extra calories. White fat stores these extra calories to use when you don’t get enough energy from food. Most of the fat in your body is white fat. You typically store it in your thighs, hips, and stomach. Too much white fat in your belly can raise your risk of heart disease and type 2 diabetes.
Brown fat and white fat are made of different things. White fat is made of big droplets of lipids, or fatty acids. Cells in brown fat are packed with mitochondria. Mitochondria are rich in iron, which gives brown fat its color. They’re the heart of your cells. They take in nutrients like sugar and white fat and break them down to make energy. Brown fat stores more energy in a smaller space than white fat does.
How It Works
When your body gets cold, it makes a hormone called norepinephrine. Brown fat has receptors for norepinephrine. When these receptors sense the hormone, they signal the many mitochondria to start churning out energy. This creates the warmth that helps you maintain your body temperature.
Although you lose most of your brown fat as you grow, you hold on to some of it. Adults have very small amounts of brown fat in the neck, collarbone, kidneys, and spinal cord. Lean people typically have more brown fat than overweight people. Women also tend to have more than men.
Brown Fat and Your Health
Scientists are researching other roles brown fat might play in your body. Specifically, they want to know more about how it uses white fat as fuel. Some studies are also looking at how exercise might signal hormones that turn on brown fat. Doctors are trying to figure out if they can use the power of brown fat to treat obesity.
One study found that brown fat filters out certain amino acids such as leucine, isoleucine, and valine from your blood. You get these amino acids from foods like eggs, meat, fish, chicken, and milk. You also get it from some muscle-building supplements. They’re good for you in normal amounts, but having too much in your blood is linked to obesity and diabetes. The less brown fat you have, the less you’re able to filter out these amino acids when their levels get too high, and your risk of these conditions goes up.
Another study looked at whether a drug could create the same reaction that cold causes in brown fat cells. The hope is that being able to trigger this reaction with medication will lead to new weight loss methods.
Treatment for obesity could help lower rates of diabetes. One area of concern is that using extra energy can raise your heart rate and blood pressure, which could raise your risk of heart problems. Researchers are working to find out how safe such a drug would be.
